In recent years, as display devices replacing liquid crystal displays, organic EL displays using self-luminous organic light emitting elements have been put into practical use. The organic EL displays are of self-luminous type, and thus have a wide viewing angle as compared with liquid crystal displays or the like and sufficient responsiveness to high definition and high speed video signals.
Regarding the light emitting elements hitherto, a trial has been carried out to improve display performance by controlling light emitted from emission layers, for example, by improving chromatic purity of emission colors or luminous efficiency through introducing a resonator structure (for example, see International Publication No. 01/39554). For example, as shown in FIG. 13, in an organic light emitting element of a top emission type where light is emitted from a surface (upper surface) opposite to a substrate, a light emitting portion Z10 has a structure where an anode electrode Z13, a organic layer Z14, and a cathode electrode Z16 are sequentially laminated via a driving transistor ZTr1, and light is multiply reflected from the organic layer Z14 between the anode electrode Z13 and the cathode electrode Z16. Here, the driving transistor ZTr1 drives the light emitting portion Z10 and constitutes a pixel driving circuit along with a signal line Z120A or the like. In addition, in FIG. 13, the reference numeral Z111 denotes a substrate, the reference numeral Z212 denotes a gate insulation layer of the driving transistor ZTr1, the reference numeral Z217 denotes a protective layer made of silicon nitride or the like, and the reference numeral Z218 denotes a planarization layer made of polyimide or the like. Also, the reference numeral Z17 denotes a metal layer which is an auxiliary line, the reference numeral Z24 denotes an aperture defining insulation layer, the reference numeral Z18 is a protective layer made of silicon nitride or the like, and the reference numeral Z19 denotes a sealing substrate made of a transparent material.
In addition, in a typical organic EL display, as shown in FIG. 13, the organic light emitting element Z10 has a sterical shape with concave and convex in the laminated direction in the emission region, not a planarized shape. For this reason, if the external light LIN is incident on the light emitting portion Z10, the reflected light LR other than specular light causes diffraction phenomenon, and thus a viewer may see unwanted rainbow colored light according to positions of the viewer. There is a problem in that this unnecessary rainbow colored light interferes within the organic light emitting elements in a pixel or within adjacent pixels and may be strengthened at a specific angle.
Specifically, the intensity of the reflected light LR may increase if satisfying the following conditional equation (1), and the intensity of the reflected light LR may decrease if satisfying the following conditional equation (2). Here, m is an integer value, λ is a wavelength, P is a pitch of arranged pixels, and θ is an angle of the reflected light LR with respect to the specular light.m·λ=P·sin θ  (1)(m+½)·λ=P·sin θ  (2)
The occurrence of the interference greatly hinders the viewer from recognizing the originally displayed image.
This sterical shape is caused by the existence of lines such as the signal line Z120A in addition to the driving transistor ZTr1, which are positioned in the lower layer of the light emitting portion Z10. Therefore, if the protective layer Z217 or the planarization layer Z218 covering the pixel driving circuit is made sufficiently thick, the upper surface of the planarization layer Z218 on which the light emitting portion Z10 is formed and thus a planarized surface with high accuracy can be obtained. Therefore, the planarity of the light emitting portion Z10 is naturally improved. However, in that case, the thickness of the entire device increases, and thus there is a problem in that the intrinsic advantage of the organic EL display which is thinner than the liquid crystal display and the like may not be utilized.
It is desirable to provide a display device which is thin and can achieve better image display performance.